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Paralleling 9V batteries?

Discussion in 'Electronic Design' started by T. Ryan, Dec 21, 2004.

  1. T. Ryan

    T. Ryan Guest

    I need longer battery life than a single 9V provides.

    What is the conventional wisdom on wiring two or more in parallel,
    particularly since any two could not be expected to have exactly the
    same charge?

    Advisable or not? If not, any way around it by adding certain passive
    components.

    Thank you,

    Tom Ryan
     
  2. Guest

    A 9V battery is essentially six watch batteries stacked in a metal can.
    It is more efficient and easier to move to six 'AAA' cells than to use
    two 9V batteries.
     
  3. Anders F

    Anders F Guest

    Not! I second the six standard elements approach =)
    Two diodes will do the trick. But you'll loose voltage
    (=>power=>efficiency)...

    /Anders
     
  4. James Meyer

    James Meyer Guest

    If the batteries are ordinary alkaline or carbon/zinc types, then
    paralleling with no extra circuitry is perfectly all right with no potential
    problems regardless of their state of charge.

    If the batteries are rechargable, NiCad or Lithium, they can be
    paralleled with no extra circuitry if both batteries are new and both are
    charged to the same state before being paralleled.

    Jim
     
  5. Ben Bradley

    Ben Bradley Guest

    A 'good' way is to add a a diode (or "rectifier" depending on
    current used) in series with each battery, so the higher voltage (and
    more fully charged) battery will provide the most current, and no
    current (other than a little reversed-bias diode leakage,
    insignificant) will flow from one battery to the other.
    If near-full battery voltage or high efficiency is important, the
    0.6V drop of regular silicon diodes can be reduced to about 0.2V by
    using Schottky diodes.

    If this is a one-off project, the above should be fine, but if it's
    a production product I would think the solution is a bigger single
    battery (I have never ever seen a product that had two batteries in
    parallel) or string of cells in series, such as six AAA or AA 1.5V
    cells.
     
  6. Mark Jones

    Mark Jones Guest

    I'd like to add that Schottky diodes have significantly higher
    reverse leakage current. No such thing as a free lunch. :)
     
  7. Chris Carlen

    Chris Carlen Guest


    They can also have more voltage drop than 0.2V when large currents pass.
    For ex., an SR304 rated 40V 3A drops about 0.43V with 3A of current.

    --
    _______________________________________________________________________
    Christopher R. Carlen
    Principal Laser/Optical Technologist
    Sandia National Laboratories CA USA
    -- NOTE: Remove "BOGUS" from email address to reply.
     
  8. Ian Stirling

    Ian Stirling Guest

    Hardly easier to change.
     
  9. lemonjuice

    lemonjuice Guest

    Batteries connected in series last longer though you're getting less
    Ah. The parallel connection drives current through each other when not
    operating and this tends to destroy them earlier. You though need to
    take into account though the costs of the 6 AAs against the 2 9V's.
     
  10. Mark Zenier

    Mark Zenier Guest

    You can get battery holders that hold 6 AA cells and use the same
    snap connector as a 9 volt cell.

    Philmore BH3634, $1.19 at Frys
    (or cheaper at All Electronics).

    Radio Shack, for some reason, only sell ones that have 4 or 8 cells.

    Mark Zenier Washington State resident
     
  11. Guest

    Ever take apart a nine volt battery? It is six little cells wired in
    series.
    Nine volt batteries are costlier by the watt-hour than buying cells and
    putting them
    together in series yourself.
    Any cells from AAA to D offer better power to the dollar than the
    nine-volt package.
     
  12. Jon Yaeger

    Jon Yaeger Guest


    Yeah, but the cost of the sockets detract from the savings.
     
  13. kam

    kam Guest

     
  14. I read in sci.electronics.design that wrote (in
    NiCd batteries have seven cells. 7 x 1.2 = 8.4, which is considered near
    enough to 9 V for marketing.
     
  15. And the reason that 9 volt batteries are not being used in new designs
    is that AA cells offer significantly better power density.
    --
    Many thanks,

    Don Lancaster
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    voice: (928)428-4073 email:

    Please visit my GURU's LAIR web site at http://www.tinaja.com
     
  16. Jeff

    Jeff Guest

    Not the ones I've owned - they were 7.2V, made from 6 cells. But then again,
    I haven't bought a new 9V NiCd in a few years since the few things I own
    that need a 9V battery, should have alkalines installed due to the low drain
    nature of the products, such as alarm clock back up, DMM batteries, smoke
    alarms, etc. Even the newer Fluke DMM's now use AA's.
     
  17. Dave VanHorn

    Dave VanHorn Guest

    I've seen 7.2 and 8.4V versions, but the 7.2, made from six slim cylindrical
    cells is more common.
    The 8.4 is seven button cells.

    It's pretty much a waste though, to power a 5V system from 9V, especially if
    it draws any significant current. Switchers help, but there are low current
    ranges where the linears are more efficient than the switchers.
     
  18. budgie

    budgie Guest

    Only once.
     
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